Various surveys and experimental work have been conducted by the present inventor, and possibly others, of ways and means for "freezing" magnetically recorded data in order both to preserve the data from accidental erasure and to maintain security of the data against deliberate attack or unauthorized modification. Much of such surveying and experimental work previously has been concentrated on the protection of magnetic data recording tapes.
Accordingly, the present inventor is aware of past proposals employing direction-controlled or modulated electron beams, lasers or other sources of radiant-beam energy to cause irreversible local destruction or modification of a magnetic track under computer control to produce magnetically recognizable trains of data pulses. The equipment required to practice such methods is costly and complex. The present inventor also is aware of the possibility of simply printing separated magnetic ink marks in one of the more or less standard magnetic data recording patterns. While a method of this type may be more attractive than the use of an electron beam, laser or similar technique, the same comments apply as to cost and complexity, particularly in respect to equipment adjustment and maintenance.
Simple mechanical embossing of a magnetic surface may be performed at relatively low speeds by selectively driving a small impact tool into the magnetic coating in accord with a computer-programmed pattern.
There exists a proposal to modify the content of passports issued by the United States, and by other countries.
According to that proposal the new passport, measuring approximately 88 mm by 125 mm, is to remain in book form. An unalterable magnetic zone is to be located either on an inside cover of the passport or on the reverse of an insert data page laminated in the passport book. The data to be encoded and later made permanent in the magnetic zone will correspond with that in the accompanying clear print and will consist of about 92 alphanumeric characters.
It is presently intended, although not certain, that in the United States the blank passport book will be printed by the Government Printing Office and delivered later to the Passport Office. If possible, it is desired that the new magnetic stripe or zone, in blank form, will be printed in the book at the time of its manufacture. At the time of issuance, the Passport Office will incorporate the bearer's personal data and photograph into the book. At the same time the new magnetic zone will be encoded automatically with the same or related data. This will be performed by entering the data into a computer, reformatting the data in the computer and causing the computer both to print the data in the passport and to output the same data to a magnetic encoding station which will encode the passport's magnetic zone. The procedures involved in producing the blank passport, later encoding (and proofreading) the magnetic zone and final "freezing" of the recorded data must be economically practical. It is especially essential that the reproduction device used to read the magnetically coded data shall be of low cost and simple design to enable easy and rapid machine reading at the automatic reading terminal.
There is a requirement that the minimum life expectancy of the "frozen" magnetic zone be 8 years. It should be noted that this life expectancy is comparable with existing ordinary magnetic recording materials and procedures.
It is also a requirement that the passport magnetic encoding be reliably readable at temperatures from -10.degree. C. to +50.degree. C. It is further required that the final form of the magnetically encoded passport withstand storage temperatures between -35.degree. C. and +80.degree. C., without degradation of performance. While this latter requirement is not always met by magnetic recording materials now in common use, it is possible to achieve the storage and reading temperature requirements by a judicious choice of the substrate material as well as the magnetically active zone.
Together with the above temperature survival requirements, the passport and its magnetic encoding is to remain reliably readable at relative air humidities between 5% and 95% with a maximum wet-bulb temperature of 25.degree. C. For storage, the required humidity excursion may be extended between the ranges of 0% and 100% without degradation of performance. Again, while many common magnetic recording media may experience difficulty in withstanding extended storage over the stated combined temperature and humidity ranges, this difficulty can be overcome reliably through appropriate choice of the materials of both the magnetic zone and its substrate.